MORPHOLOGY OF THE OWLS. 5 



utilized to complete the mouth of the meatus by joining with the tympanic recess 

 and closing the notch in question. 



The position of the obliterated paroccipital notch is indicated by a foramen, for the 

 passage of a branch of the sinus venosus, which can be traced ujiwards and forwards to 

 its mouth on the inner side of the articulation for the quadrate. Midway between this 

 foramen and the occipital condyle lies the vagus foramen, and mesiad of the vagus lie 

 the condyloid foramina. 



The basipterygoid processes are represented by two very short stout pillars rising from 

 the base of the parasphenoidal rostrum, which is of considerable breadth. In the 

 Strigidte these processes are much reduced in length, so as to be little more than 

 prominences. 



The jDre-condylar fossa is well marked. 



The parasphenoidal rostrum of the Striges presents some interesting modifications. 

 Apart from its great breadth at the base, which appears to be characteristic of the 

 Owls, the parasphenoid, in the majority of the Asionidse, has undergone a very con- 

 siderable shortening, terminating at the level of the palato-pterygoid articulation, instead 

 of running forward to terminate just above the hinder end of the maxUlo-palatine 

 processes, as in the Ealconiformes, for example. This abbreviation of the rostrum is also 

 noticeable in the Caprimulgi. 



Among the Owls, however, Surnia has a relatively long rostrum, since it terminates 

 midway between the pterygo-palatine articulation and the hinder border of the maxillo- 

 palatine processes. The Strigidae appear also to have an abbreviated rostrum, but until 

 I have an opportunity of examining nestlings I cannot settle this point, owing to the 

 extraordinary inflation of the tissues of this part of the skull. 



The Lateral Surface of the Cranium. — The tympanic cavity is unusually large in the 

 Striges, and presents some interesting modifications. Studied in its least specialized 

 condition, the increased size of this cavity is found to be due to the great develo^iment 

 of the tympanic wing of the exoccipital and the external border of the squamosal, 

 the outgrowths from these two bones forming a conspicuous outstanding wing of 

 varying shape, according to the genera examined. The squamosal portion of the wing it 

 is to be noted is borne by the region corresponding to the squamosal prominence of the 

 Ealconiform skull, a prominence generally more conspicuous among the Owls, in the 

 nestling skull; its presence in the adult skull is marked by the great thickening of 

 the skull-walls by the development of pneumatic tissue, a thickening which causes the 

 quadrate in the adult Striges to appear to be set much nearer the middle line than in the 

 nestling. 



Not only is the tympanic cavity proper actually increased in size by the development 

 of the lateral wings above described, but a more or less perfect chamber is added thereto 

 by the outward extension of that portion of i\w wing which arises from the region of the 

 squamosal prominence. This additional chamber is especially well developed in a few 

 generate be described presently. 



It may be studied in its simplest form perhaps in Syrnium aluco or Surnia funerea. 

 Here it forms a vestibule, opening forwards into a deep trough formed by the large post- 



